Phosphate removal via biological process coupling with hydroxyapatite crystallization in alternating anaerobic/aerobic biofilter reactor

In this work, a laboratory-scale alternating anaerobic/aerobic biofilter (A/O BF) filled with self-made steel slag media was constructed, where the integrated biological and crystalline phosphorus removal process was realized to remove phosphorus and achieve phosphorus recovery from wastewater. Phosphorus accumulating organisms (PAOs) were successfully enriched within 30 days operation, the maximum phosphate removal efficiency was close to 80% under the optimal conditions with the anaerobic time of 34 h, HRT of 4 h and influent COD of 300 mg/L. The analysis of SEM-EDS and XRD indicated that hydroxyapatite (HAP) crystals were formed inside biofilms without addition of chemical reagents. The high phosphate environment created by PAOs and the release of Ca²⁺ from the steel slag media might be responsible for the generation of HAP. These findings have crucial implications for the application BF technology to remove and recover phosphorus from wastewater.

Remarkable phosphate recovery from wastewater by a novel Ca/Fe composite: Synergistic effects of crystal structure and abundant oxygen-vacancies

Calcium-based materials are considered to be promising adsorbents for phosphate removal in the water environment due to their environmental friendliness and low price. However, improving the efficiency and rate of P adsorption of calcium-based materials still needs further exploration. In this study, a high-efficiency and eco-friendly Ca/Fe composite was rationally designed and fabricated by a co-precipitated method. Batch adsorption experiments showed that Ca/Fe composites with a Ca: Fe molar ratio of 3: 1 exhibited a remarkable phosphate sorption capacity of 161.4 mg P/g. Furthermore, the phosphate adsorption capacity of Ca/Fe-3/1 composite was maintained relatively high at pH 3-11 due to the ligand exchange, electrostatic and chemical precipitation. In addition, the experiment performed to determine the effect of coexisting ions shows that only carbonate ions slightly inhibit the phosphate adsorption effect of the Ca/Fe-3/1 composite. The newly prepared Ca/Fe composites have a fast phosphate removal efficiency. The XPS and EPR analysis showed that a large number of oxygen vacancies were formed on Ca/Fe composites due to the introduction of magnetic Fe. This is the first time to introduction oxygen vacancies into Ca/Fe composites by co-precipitation. The existence of oxygen vacancies can promote electron transfer rate and reduce the bonding energy barrier for phosphate adsorption, thereby increasing the phosphate absorption rate of the Ca/Fe composites. The enhanced phosphate removal by Ca/Fe composites with abundant oxygen vacancies provides a new strategy for the preparation of commercial phosphate -controlling materials.

Performance of a recirculating aquaculture system using biofloc biofilters with convertible water-treatment efficiencies

To achieve high water-treatment efficiencies and simplify the setup of recirculating aquaculture systems (RAS), this study examined the use of suspended growth reactors (R1 and R2) based on biofloc technology (BFT) as water-treatment biofilters. Moreover, the conversion of the heterotrophic R1 biofilter to a nitrifying role was investigated. During RAS operation using heterotrophic BFT biofilters, R1 and R2 simultaneously controlled total ammonium nitrogen, nitrite (NO₂^--N), nitrate (NO₃^--N), soluble reactive phosphate (SRP), and alkalinity, with relevant functional microbes including denitrifying bacteria (DNB), phosphorus accumulating organisms (PAOs), denitrifying PAOs (DNPAOs), glycogen accumulating organisms, ammonia oxidizing bacteria, and nitrite oxidizing bacteria. To achieve low concentrations of nitrogen, phosphorus, and save carbon sources, we were able to quickly convert R1 into a nitrifying BFT biofilter by stopping carbohydrate addition. Although there were dominant relative abundances of DNB, PAOs, and DNPAOs in the converted R1, the lack of carbon sources resulted in continuous rise of NO₃^--N in the effluent, stable NO₂^--N removal efficiency, and absence of SRP removal after 40 h. However, R2 retained the previous NO₃^--N and SRP removal efficiencies with carbohydrate addition. This indicated that this novel RAS using BFT biofilters achieved simultaneous nitrogen and phosphate removal, and that the convertible water-treatment efficiencies of BFT biofilters could be controlled by carbohydrate addition. This approach could simplify the RAS setup and meet real-time water quality demands.

Modification and Validation of the Phosphate Removal Model: A Multicenter Study

BACKGROUND

Our research group has previously reported a noninvasive model that estimates phosphate removal within a 4-h hemodialysis (HD) treatment. The aim of this study was to modify the original model and validate the accuracy of the new model of phosphate removal for HD and hemodiafiltration (HDF) treatment.

METHODS

A total of 109 HD patients from 3 HD centers were enrolled. The actual phosphate removal amount was calculated using the area under the dialysate phosphate concentration time curve. Model modification was executed using second-order multivariable polynomial regression analysis to obtain a new parameter for dialyzer phosphate clearance. Bias, precision, and accuracy were measured in the internal and external validation to determine the performance of the modified model.

RESULTS

Mean age of the enrolled patients was 63 ± 12 years, and 67 (61.5%) were male. Phosphate removal was 19.06 ± 8.12 mmol and 17.38 ± 6.75 mmol in 4-h HD and HDF treatments, respectively, with no significant difference. The modified phosphate removal model was expressed as Tpo4 = 80.3 × C45 - 0.024 × age + 0.07 × weight + β × clearance - 8.14 (β = 6.231 × 10-3 × clearance - 1.886 × 10-5 × clearance2 - 0.467), where C45 was the phosphate concentration in the spent dialysate measured at the 45th minute of HD and clearance was the phosphate clearance of the dialyzer. Internal validation indicated that the new model was superior to the original model with a significantly smaller bias and higher accuracy. External validation showed that R2, bias, and accuracy were not significantly different than those of internal validation.

CONCLUSIONS

A new model was generated to quantify phosphate removal by 4-h HD and HDF with a dialyzer surface area of 1.3-1.8 m2. This modified model would contribute to the evaluation of phosphate balance and individualized therapy of hyperphosphatemia.

Lanthanum molybdate/magnetite for selective phosphate removal from wastewater: characterization, performance, and sorption mechanisms

Lanthanum molybdate/magnetite (M-La₂(MoO₄)₃) with various LaCl₃/Fe₃O₄ mass ratios was synthesized and optimized for selective phosphate removal from wastewater. M-La₂(MoO₄)₃ (2:1) was selected on the basis of phosphate sorption capacity for further experiments and characterized by a variety of methods. The phosphate sorption kinetics, isotherms, and matrix effect were studied. The maximum sorption capacity at initial pH 7 indicates the possible applicability M-La₂(MoO₄)₃ (2:1) in removing phosphate from the aquatic environment. Phosphate removal by M-La₂(MoO₄)₃ (2:1) with high selectivity was achieved in the presence of other co-existing anions, while calcium and magnesium ions were found to inhibit the sorption process. The sorption isotherm study showed that Freundlich and Sips models fit better the Langmuir model, indicating that heterogeneous multilayer sorption was dominant during the phosphate sorption process. Sorption kinetic results showed that the pseudo-first-order kinetic model can describe well the phosphate sorption process by M-La₂(MoO₄)₃ (2:1). Consecutive sorption-desorption runs showed that M-La₂(MoO₄)₃ (2:1) could be reused for a few cycles. Simultaneous removal of phosphate and organic matter was achieved in real wastewater by using M-La₂(MoO₄)₃ (2:1). The sorption mechanism was inner-sphere complexation.

Comparative investigation of characteristics and phosphate removal by engineered biochars with different loadings of magnesium, aluminum, or iron

Engineered biochars (EBCs) loaded with metal oxides/hydroxides have been used as sorbents to remove and recycle phosphate (P) from wastewater. However, P removal by EBCs made with different types and loading of metals have rarely been compared in a single study. Thus, in this study, EBCs were synthesized through pyrolysis of bamboo or hickory wood chips (25 g) pretreated with four amounts (25, 50, 75, and 100 mmol) of magnesium (Mg), aluminum (Al), or iron (Fe) salt solutions (Mg-EBC, Al-EBC, and Fe-EBC, respectively). The resulting EBCs were loaded with metal oxides/hydroxides that served as P adsorption sites. Al-EBCs showed the highest aqueous stability with little metal dissolution, which can be attributed to the low level of residual (unconverted) metal salt as well as the extremely low solubility of loaded Al metal oxyhydroxide. After the leaching/washing, the metal loading efficiencies of the Al- and Mg-EBCs were similar (50-60%) and stable metal loadings increased with pretreatment salt amounts, indicating that the amount of the two metal oxides/hydroxides in the EBCs can be controlled during pretreatment. However, stable iron oxide on the Fe-EBCs remained almost the same for all the four levels of pretreatment, reflecting saturation of the biochar surface. All the EBCs showed increasing P adsorption with increasing metal loading. At low initial P concentrations of 31 mg/L, Fe- and Al-EBCs removed up to 68% and 94% of P, likely through an electrostatic interaction mechanism. At high P concentrations, Mg-EBC had the largest P adsorption capacity (119.6 mg P/g), mainly through the combination of surface precipitation and electrostatic interaction mechanisms. This study demonstrates that metal oxide/hydroxide-loaded EBCs are promising sorbents that can be designed to meet specific needs for the removal of aqueous P in various applications.

Stability of magnetic LDH composites used for phosphate recovery

Layered double hydroxides (LDH) and their magnetic composites have been intensively investigated as recyclable high-capacity phosphate sorbents but with little attention to their stability as function of pH and phosphate concentration. The stability of a Fe₃O₄@SiO₂-Mg₃Fe LDH P sorbent as function of pH (5-11) and orthophosphate (P_i) concentration (1-300 mg P/L) was investigated. The composite has high adsorption capacity (approx. 80 mg P/g) at pH 5 but with fast dissolution of the LDH component resulting in formation of ferrihydrite as evidenced by Mössbauer spectroscopy. At pH 7 more than 60% of the LDH dissolves within 60 min, while at alkaline pH, the LDH is more stable but with less than 40% adsorption capacity as compared to pH 5. The high P_i sorption at acid to neutral pH is attributed to P_i bonding to the residual ferrihydrite. Under alkaline conditions P_i is sorbed to LDH at low P_i concentration while magnesium phosphates form at higher P_i concentration evidenced by solid-state ³¹P MAS NMR, powder X-ray diffraction and chemical analyses. Sorption as function of pH and P_i concentration has been fitted by a Rational 2D function allowing for estimation of P_i sorption and precipitation. In conclusion, the instability of the LDH component limits its application in wastewater treatment from acid to alkaline pH. Future use of magnetic LDH composites requires substantial stabilisation of the LDH component.

Performance analysis of hydrated Zr(IV) oxide nanoparticle-impregnated anion exchange resin for selective phosphate removal

The superior removal selectivity of hydrated zirconium oxide nanoparticle-impregnated porous anion exchange resin (ZAE) highlights its use as phosphate removal adsorbent. However, most research examines selective phosphate removal performance using randomly determined single content of hydrated zirconium oxide, and thus the use of the ZAE in real applications remains limited. Therefore, this study aimed to investigate the selective phosphate removal performance of ZAE with different content of hydrated zirconium oxide nanoparticle (HZO NP, represented by zirconium content) by considering various conditions. A molybdate intermediate method was devised to fabricate ZAE with high loaded HZO by weakening the Donnan exclusion to HZO precursors produced from the fixed positively charged host. Consequently, the resultant ZAE was characterized by 17.8 wt% of zirconium. ZAE exhibited an increased selectivity to phosphate against competing ions in the synthetic and simulated real water matrices for both batch and fixed-bed modes as the zirconium content of ZAE increased. High performance was retained, and regeneration led to possible reusability. The linear correlation between selective phosphate removal performances and zirconium content indicates that the zirconium content is a fundamental factor determining the ZAE phosphate adsorption removal. The HZO NPs within ZAE slow adsorption kinetics by blocking AE pores and provide specific adsorption sites for phosphate removal by inner-sphere complexation.

Network interior and surface engineering of alginate-based beads using sorption affinity component for enhanced phosphate capture

In order to alleviate the environmental problems caused by excessive discharge of phosphate, an environmental friendly and highly efficient bio-sorbent (SA-La@PEI) for phosphate was fabricated by combing strategies of sorption affinity component mediated and poly(ethylenimine) surface engineering of alginate beads. Various characterization methods like SEM, FTIR, XRD and XPS were adopted to examine the morphology and functional group composition of SA-La@PEI. Through detailed tests, SA-La@PEI exhibited excellent adsorption performance of 121.2 mg/g, which was better than most published materials. More importantly, the outstanding phosphate selectivity of SA-La@PEI was exposed when NO₃^-, HCO₃^-, SO₄^2- and Cl^- were added to the phosphate solution. Considering the integrated components in composites, both chemical precipitation and electrostatic attraction can be considered as the dominant mechanisms of phosphate adsorption. Totally, as-prepared SA-La@PEI beads might be a promising sorbent for the decontamination of excessive phosphate because of its low-cost, excellent adsorption performance and mechanical strength.

Properties of CaO2 for H2O2 release and phosphate removal and its feasibility in controlling Microcystis blooms

Calcium peroxide (CP) has been widely applied in environmental remediation, but few studies have reported its application in controlling Microcystis blooms. To recognize its feasibility for mitigating Microcystis blooms, the properties of CP in terms of hydrogen peroxide (HP) release and phosphate removal were investigated at different CP doses, temperatures, and initial pH values. HP release kinetics followed the Higuchi model. Batch experiments conducted in this study suggested that the HP yield and release rate were positively correlated with the CP dose. Increasing temperature decreased the HP yield but accelerated the HP release rate. The phosphate removal kinetics were well simulated by the pseudo-second-order model. The batch experiments suggested that an increased CP dose enhanced the phosphate removal capacity, but it did not affect the phosphate removal rate. Moreover, increased temperature accelerated both phosphate removal capacity and rate. However, the initial pH of low-buffer-capacity solutions did not notably affect HP release and phosphate removal. According to laboratory experiments, HP released from CP could impair photosynthetic activity, resulting in Microcystis mortality. Furthermore, the reduced phosphate concentration in the solutions suggested that CP could facilitate the control of eutrophication, which directly reduced bloom formation. Hence, our results confirmed CP as a promising algicide for Microcystis bloom control, and it is worthwhile to develop novel methods for bloom mitigation based on CP. Graphic abstract.

MOFs-derived conductive structure for high-performance removal/release of phosphate as electrode material

Porous metal-organic frameworks (MOFs) have drawn increasing attention as promising phosphate adsorbents. Yet the potential agglomeration of MOFs particles and the difficult collection process largely thwarted their application. Meanwhile, adsorbents regeneration might destroy MOFs structures due to the use of strong alkaline solution. In this work, we reported a strategy for designing and fabricating an electrode to remove phosphate based on MIL-101 derived metal/carbon via a two-step carbonization step, which not only introduced C doping but also created a stable structure. With the assistance of electric field, the migration and capture of phosphate anions were greatly enhanced. Under 1 V condition, the material exhibited a high maximum removal capacity of 97.73 mg P/g. Adsorption kinetics and parameters for phosphate at different conditions were analyzed. Langmuir and Freundlich isotherms were employed to validate the adsorption data. More importantly, the regeneration of electrode was achieved in a more facile and efficient way than micro/ nanoparticles adsorbents by simple voltage control. Such an intriguing approach may provide a new platform to further expand the use of MOFs for adsorption process.

Effects of aging of ferric-based drinking water sludge on its reactivity for sulfide and phosphate removal

Recent studies demonstrated the practical potential of multiple beneficial reuse of ferric-rich drinking water sludge (ferric DWS) for sulfide and phosphate removal in wastewater applications. In practice, ferric DWS is often stored on-site for periods ranging from days to several weeks (or even months), which may affect its reuse potential through changes in iron speciation and morphology. In this study, we investigated for the first time the impact of ferric DWS 'aging' time on the iron speciation and morphology and its subsequent impact on its reactivity and overall sulfide and phosphate removal capacity. A series of coagulation tests were conducted to generate ferric DWS of a practically relevant composition by using raw influent water from a full-scale drinking water treatment plant (DWTP). A comparison with ferric DWS from 8 full-scale DWTPs confirmed the similitude. The presence of akaganeite (β-FeOOH) was detected in ferric DWS (through XRD analyses), independent of the DWS storage time. However, the morphology of akaganeite changed over time from a predominant poorly-crystalline phase in 'fresh' DWS (8 ± 0.1% of total Fe) to a highly crystalline phase (76 ± 3% of total Fe) at a sludge aging time of 30 days which was confirmed by means of Rietveld refinement in XRD analyses (n = 3). Subsequent batch tests showed that its sulfide removal capacity decreased significantly from 1.30 ± 0.02 mmol S/mmol Fe (day 1) to 0.60 ± 0.01 (day 30), a decrease of 54 % (p < 0.05). The level of crystallinity however had no impact on sulfide removal kinetics, most sulfide being removed within 10 minutes. Upon aeration of sulfide-loaded ferric DWS in activate sludge, amorphous iron oxides species were formed independent of the initial DWS crystallinity which resulted in efficient P removal at capacities similar to that of conventional FeCl₃ dosing.

Hydrogen oxidizing bacteria are capable of removing orthophosphate to ultra-low concentrations in a fed batch reactor configuration

This paper proposes the use of hydrogen oxidizing bacteria (HOB) for the removal of orthophosphate from surface water as treatment step to prevent cyanobacterial blooms. To be effective as an orthophosphate removal strategy, an efficient transfer of hydrogen to the HOB is essential. A trickling filter was selected for this purpose. Using this system, a removal rate of 11.32 ± 0.43 mg PO₄^-3-P/L.d was achieved. The HOB biomass, developed on the trickling filter, is composed of 1.25% phosphorus on dry matter, which suggests that the orthophosphate removal principle is based on HOB growth. Cyanobacterial growth assays of the untreated and treated water showed that Synechocystis sp was only able to grow in the untreated water. Orthophosphate was removed to average residual values of 0.008 mg/L. In this proof of principle study, it is shown that HOB are able to remove orthophosphate from water to concentrations that prevent cyanobacterial growth.

A novel magnesium-based oxygen releasing compound for eutrophic water remediation

Eutrophication of surface water bodies is a global problem in recent years. Dosing polluted water with oxygen releasing compounds (ORCs), especially those that can remove excessive nutrients simultaneously is regarded as one of the most economical and eco-friendly methods of treating eutrophic waters. In this study, a novel Mg-based ORC was synthesized and characterized as a magnesium hydroxide and hydrogen peroxide complex (MHHPC) with Mg to H₂O₂ ratio of 2:1. Oxygen-releasing, pH-adjusting and nutrient-removal potentials of MHHPC were evaluated in nano-pure and eutrophic water. The overall performance of MHHPC in preventing the eutrophic water from turning black and odorous was compared with the performance of other ORCs namely, MgO₂, CaO₂ and the combination of MgCl₂ and H₂O₂. The results showed that MHHPC was capable of constantly releasing oxygen to aqueous phase over a period of one week. Phosphate and ammonia nitrogen in synthetic buffered water can were removed as struvite and other precipitates from the aqueous phase. In the synthetic eutrophic water, all the ORCs tested were able to reduce aqueous ammonia nitrogen below 0.5 mM, while only CaO₂ and MHHPC successfully removed the aqueous phosphate. However, CaO₂ and MgCl₂+H₂O₂ significantly inhibited microbial activity.

Full-scale investigation of ferrous dosing in sewers and a wastewater treatment plant for multiple benefits

This study demonstrates the full scale application of iron dosing in a metropolitan wastewater treatment plant (WWTP) and the upstream sewer system for multiple benefits. Two different dosing locations, i.e., the WWTP inlet works (Trial-1) and upstream sewer network (Trial-2) were tested in this study. Both dosing trials achieved multiple benefits such as sulfide control, phosphate removal and improved sludge dewaterability. During Trial-1, a sulfide reduction of >90% was achieved at high dosing rates (>19 kgFe ML^-1) of ferrous chloride in the inlet works and in Trial-2 the in-sewer ferrous dosing had significant gas phase hydrogen sulfide (H₂S) concentration reduction in the sewer network. The ferrous dosing enhanced the phosphate removal in the bioreactor up to 76% and 53 ± 2% during Trial-1 & 2, respectively. The iron ending up in the anaerobic sludge digester reduced the biogas H₂S concentration by up to 36% and 45%, respectively. The dewaterability of the digested sludge was improved, with relative increases of 9.7% and 9.8%, respectively. The presence of primary clarifier showed limited impact on the downstream availability of iron for achieving the afore-mentioned multiple benefits. The iron dosing enhanced the total chemical oxygen demand removal in the primary clarifier reaching up to 49% at the high dose rates during Trial-1 and 42 ± 1% during Trial-2. This study demonstrated that multiple benefits could be achieved independent of the iron dosing location (i.e., at the WWTP inlet or in the network). Further, iron dosing at both locations enhances primary settling, beneficial for bioenergy recovery from wastewater.

Synthesis of magnetite/lanthanum hydroxide composite and magnetite/aluminum hydroxide composite for removal of phosphate

Two magnetic adsorbents, magnetite/aluminum hydroxide composite (MAC) and magnetite/lanthanum hydroxide composite (MLC), were successfully synthesized by a simple one-pot method and their phosphate adsorption process was investigated. The properties of synthesized adsorbents were studied using Fourier transform infrared spectroscopy (FTIR), zeta potential, vibrating sample magnetometry (VSM) and X-ray photoelectron spectroscopy (XPS). The adsorption isotherms, adsorption kinetics and the effects of solution pH and dissolved organic carbon (DOC) on the adsorption of phosphate in aqueous solution by MAC, MLC-2, MLC-10 and LMB were investigated to evaluate the difference in phosphate removal efficiency of the magnetic adsorbents and non-magnetic adsorbent. According to the results of this study, MLC-10 had a higher phosphate adsorption capacity (19.34 mg P g^-1) than LMB (11.55 mg P g^-1), MAC (10.48 mg P g^-1) and MLC-2 (8.89 mg P g^-1). MLC-10 showed a relative higher partition coefficient (PC) (1.74 mg g^-1 μM^-1) than other three adsorbents at initial P concentration of 15 mg L^-1. Also, MLC-10 was less pH dependent than MAC and had higher phosphate adsorption capacities under different DOC concentrations (0-72 mg L^-1) than LMB, MAC and MLC-2. Further, MLC-10 had excellent recyclability due to high magnetism. Electrostatic interaction and the inner-sphere surface complexation were the potential phosphate adsorption mechanisms employed by MLC-10. In summary, MLC-10 is a promising adsorbent for phosphate removal from eutrophication water.

Total recycle strategy of phosphorus recovery from wastewater using granule chitosan inlaid with γ-AlOOH

Eutrophication which caused by excessive phosphorus in aquatic environment is a worldwide problem. Phosphorus is a nonrenewable resource widely used in agriculture and industry. Therefore, the development of economical methods for phosphorus capture and reuse from wastewater is urgently needed. In this study, a novel granule chitosan inlaid with γ-AlOOH on its structure (γ-AlOOH@CS) was prepared for phosphate removal with a recycle manner. Results showed that γ-AlOOH@CS exhibited a fast phosphate removal of 0.5 h for half adsorption capacity. The material presented a high adsorption capacity of 45.82 mg/g, the adsorption capacity maintained stability at pH 4-6, and favorable selectivity was observed when compared with other common anions. Column experiment was also performed well in treatment of the simulated wastewater. Isotherms and thermodynamics studies indicated that phosphate adsorption onto γ-AlOOH@CS was heterogeneous, spontaneous and exothermic. In material recycle experiment, by using NaOH solution as solvent and phosphoric acid as precipitant under hydrothermal reaction conditions, the products of chitosan, aluminum phosphate and sodium dihydrogen phosphate were obtained, with their purity reaching the industrial standard. Meanwhile, chitosan can be reused for new γ-AlOOH@CS preparation. This study provides a total recycle strategy of phosphorus removal from wastewater.

Enhanced phosphate removal using zirconium hydroxide encapsulated in quaternized cellulose

Zirconium-based materials are efficient adsorbent for aqueous phosphate removal. However, current zirconium-based materials still show unsatisfied performance on adsorption capacity and selectivity. Here, we demonstrate a zirconium hydroxide encapsulated in quaternized cellulose (QC-Zr) for the selective phosphate removal. Zirconium hydroxide nanoparticles were simultaneously generated in situ with the QC framework and firmly anchored in the three-dimensional (3D) cross-linked cellulose chains. The maximum P adsorption capacity of QC-Zr was 83.6 mg P/g. Furthermore, the QC-Zr shows high P adsorption performance in a wide pH range, generally due to the electrostatic effects of quaternized cellulose. The enhanced adsorption of P was also achieved in the presence of competing anions (including Cl^-, NO₃^-, SO₄^2-, SO₄^4-) and humic acid (HA) even at a molar ratio up to 20 levels. The column adsorption capacity of QC-Zr reached 4000 bed volumes (BV) at EBCT = 0.5 min as the P concentration decreased from 2.5 to 0.5 mg/L. Mechanism study revealed that both -N⁺(CH₃)₃ groups and zirconium hydroxide were involved in phosphate adsorption via electrostatic interactions between -N⁺(CH₃)₃ and phosphate, and the formation of zirconium hydrogen phosphate (Zr(HPO₄)x). The ³¹P nuclear magnetic resonance (NMR) study implied that P surface-precipitated and inner-sphere complexed with zirconium hydroxide at a ratio of 3:1.

Phosphate removal from industrial wastewater through in-situ Fe2+ oxidation induced homogenous precipitation: Different oxidation approaches at wide-ranged pH

Phosphate removal through in-situ Fe²⁺ oxidation induced homogenous phosphate precipitation has shown its advantages in municipal wastewater treatment. Its feasibility and suitability for phosphate removal in industrial wastewater with wide-range pH variation like electro-plating wastewater were investigated in bench scale experiments using synthetic wastewater and continuous experiment using real wastewater. Bench scale experiments showed that different Fe²⁺ oxidation approaches worked well for phosphate removal at varied pH conditions. Sole dosing Fe²⁺ salt with aeration achieved sound phosphate removal at alkaline condition (pH ≥ 8). At neutral pH (6 < pH < 8), transition metallic ions catalytic oxidation is a suitable alternative. Cu²⁺ exhibited superior catalytic Fe²⁺ oxidization over Mn²⁺, Zn²⁺, and Ni²⁺. At acid pH (3.0 ＜ pH ≤ 6.0), Fenton reaction oxidation (H₂O₂ = 5 mg/L) showed its efficiency. At their corresponding optimal pH conditions and with Fe²⁺/P ratio of 1.8, dosing sole Fe²⁺ salt, Cu²⁺ catalyzed Fe²⁺ oxidation, and Fe²⁺/H₂O₂ treatments can achieve the TP discharge limit of 0.5 mg/L. In a 30-day continuous experiment using real electro-plating wastewater (pH 4.9-5.5), in both direct Fe²⁺/H₂O₂ treatment and Cu²⁺ catalyzed Fe²⁺ oxidation treatment after wastewater pH being adjusted to 7 effluent TP met China's discharge requirement 0.5 mg/L.

Selective and efficient sequestration of phosphate from waters using reusable nano-Zr(IV) oxide impregnated agricultural residue anion exchanger

There is an urgent need to develop low-cost and effective adsorbents for enhanced removal of phosphate from contaminated waters. In this study, nanosized Zr(IV) oxide particles were immobilized on the amino modified corn staw (MCS) to fabricate a novel nanocomposite (Zr@MCS) with superior application capability. Compared with the widely used commercial anion exchangers in previous studies, the modified agricultural residue was empolyed as the host to avoid the high costs and secondary pollution in the preparation. Zr@MCS displayed remarkable selective removal of phosphate from water even in the presence of coexisting anions (Cl^-, SO₄^2-, NO₃^-) at high levels, as well as with a high adsorption capacity, fast adsorption kinetics and high availability in the wide range of pH 2-8 toward phosphate. The excellent adsorption performance of Zr@MCS is attributed to the synergistic effect of the electrostatic attraction of the quaternary ammonium groups fixed on the host skeleton and the specific adsorption of phosphate derived from the hydroxyl functional groups of Zr(IV) oxide. The exhausted Zr@MCS can be effectively regenerated by 5% NaOH-NaCl solution for sustainably utilized, and phosphorus in the desorption effluent could be recovered as high-quality struvite by a simple struvite recovery process. Furthermore, the considerable treatment volume for the synthetic solution and real wastewater in a fixed-bed flow system indicated that Zr@MCS is of great potential for phosphate removal in practice.

Adsorption and recovery of phosphate from water by amine fiber, effects of co-existing ions and column filtration

A weak-base adsorption fiber, acrylic amine fiber (AAF), was prepared for removal and recovery of phosphate from water. The adsorption properties of the AAF for phosphate and effects of co-existing ions were investigated using batch and column filtration experiments, scanning electron microscope, and Fourier transform infrared techniques. Experimental results showed that AAF had a high phosphate adsorption capacity of 119 mg/g at pH 7.0. The effects of calcium, sulfate, carbonate, nitrate, and fluoride showed that sulfate and calcium inhibited phosphate adsorption. However, AAF showed higher binding affinity toward phosphate than sulfate. Column filtration results showed that AAF could filter 1420 bed volumes of tap water containing 1.0 mg-P/L of phosphate. The saturated AAF could be regenerated using 0.5 mol/L hydrochloric acid solution and reused. After desorption, phosphate was recovered through precipitation of hydroxyapatite (Ca₅(PO₄)₃OH). The easy of regeneration, good adsorption performance, and the fiber morphology of AAF make it an attractive alternative for phosphate recovery from multiple water sources.

Probing the efficiency of magnetically modified biomass-derived biochar for effective phosphate removal

Characterization of the driving forces for effective and economical phosphate (PO₄^3-) removal from wastewater by using magnetically modified biochar was performed in this study. The biochar produced from slow pyrolysis of local agricultural biomass (wood and rice husks) were magnetically modified by co-precipitation of Fe(II) and Fe(III) ions in their presence. The surface characteristics before and after modification and their efficacy for PO₄^3- sorption, and desorption were compared. Results show that, even though magnetic biochar surface modification slightly decreased their surface area, PO₄^3- adsorption to the modified biochars was almost double (25-28 mg g^-1) than that to the raw biochar (12-15 mg g^-1). The adsorption isotherm of raw biochars was better simulated via the Langmuir model, while that of modified biochars was better fitted to the Freundlich model. Moreover, the integrated analysis by XRD, EDX, and FTIR show that PO₄^3- sorption to modified biochars could be attributed to the simultaneously-occurring electrostatic attraction, surface precipitation, and ligand exchange. While the electrostatic attraction was dominant in the presence of unmodified biochars. The regenerated modified biochars retained substantial PO₄^3- adsorption capacity up to several regeneration cycles. Their high reusability potential leads to the effective and economical phosphate recovery and thus modified biochars could offer a viable strategy for PO₄^3- removal.

Function integrated chitosan-based beads with throughout sorption sites and inherent diffusion network for efficient phosphate removal

A novel, cost-effective and biomass-derived adsorbent was fabricated by coating polydopamine on lanthanum-chitosan hydrogel (La-CS@PDA), which were endowed with a plentiful of amine groups. The diffusion structure of channel-network of La-CS@PDA made it well used in phosphate removal in wastewater treatment. The Langmuir isotherm delivered the maximal adsorption capacity about 195.3 mg/g, which was superior to most reported phosphate removal materials. More significantly, in the presence of competitive anions Cl^-, SO₄^2-, HCO₃^-, NO₃^-, F^- and HCrO₄^-, the resultant La-CS@PDA still conducted distinct selectivity for phosphate, which could be attributed to the selective binding sites of La species in the composite. Under continuous adsorption, the dynamic experimental data fitted well with Thomas model which imitates industrial practical application. By virtue of more fortes of high efficiency, ease of separation and expectable mechanical strength, as-prepared La-CS@PDA might be a promising candidate of dephosphorizing sorbent.

Opportunities for reducing coagulants usage in urban water management: The Oxley Creek Sewage Collection and Treatment System as an example

Iron and aluminium based coagulants are used in enormous amounts and play an essential role in urban water management globally. They are dosed at drinking water production facilities for the removal of natural organic matter. Iron salts are also dosed to sewers for corrosion and odour control, and at wastewater treatment plants (WWTPs) for phosphate removal from wastewater and hydrogen sulfide removal from biogas. A recent laboratory study revealed that iron dosed to sewers is available for phosphate and hydrogen sulfide removal in the downstream WWTP. This study demonstrates for the first time under real-life conditions the practical feasibility and effectiveness of the strategy through a year-long full-scale investigation. Over a period of 5 months, alum dosing at ∼190 kg Al/day to the bioreactor in a full-scale WWTP was stopped, while FeCl₂ dosing at ∼160 kg Fe/day in the upstream network was commenced. Extensive sampling campaigns were conducted over the baseline, trial and recovery periods to investigate sulfide control in sewers and its flow-on effects on phosphate in WWTP effluent, H₂S in biogas, as well as on the WWTP effluent hypochlorite disinfection process. A plant-wide mass balance analysis showed that the Fe²⁺ dosed upstream was effectively used for P removal in the activated sludge tanks, with an effluent phosphate concentration comparable to that in the baseline period (i.e. with alum dosing to the bioreactor). Simultaneously, hydrogen sulfide concentration in biogas decreased ∼43%, from 495 ± 10 to 283 ± 4 ppm. No effects on biological nitrogen removal and disinfection processes were observed. Both effluent phosphate and H₂S in biogas increased in the recovery period, when in-sewer dosing of FeCl₂ was stopped. X-ray diffraction failed to reveal the presence of vivianite in the digested sludge, providing strong evidence that thermal hydrolysis prevented the formation of vivianite during anaerobic digestion. The latter limits the potential for selective recovery of Fe and P through magnetic separation. Overall, our study clearly demonstrates the multiple beneficial reuse of iron in a real urban wastewater system and urges water utilities to adopt an integrated approach to coagulant use in urban water management.

Magnetic polymer-supported adsorbent with two functional adsorption sites for phosphate removal

In this paper, a new magnetic polymer-supported phosphate adsorbent MPVC-EDA-Ce was prepared by loading cerium (hydr)oxides onto ethylenediamine-functionalized polyvinyl chloride for the first time. MPVC-EDA-Ce showed excellent adsorption performances towards phosphate and easy recovery. The adsorption isotherm and kinetics of MPVC-EDA-Ce followed Langmuir monolayer model and the pseudo-second-order model, respectively. The pH results demonstrated that the MPVC-EDA-Ce could effectively remove phosphate in a wide range of pH with insignificant cerium leaching. Furthermore, analyses on adsorption mechanism and effect of competing anions demonstrated the formation of strong inner-sphere complexation between cerium (hydr)oxides and phosphate, which was a selective adsorption process, while positively charged quaternary ammonium groups adsorbed phosphate via relatively weak electrostatic attraction which was a non-selective adsorption process. The study provided a good reference to design novel phosphate adsorbents with two even more functional adsorption sites and a deep insight to investigate the adsorption mechanism towards phosphate.

Immobilization of mercury using high-phosphate culture-modified microalgae

This study developed a novel Hg(II) immobilization strategy by firstly incubating algal cells in high-phosphate cultures for surface modification, followed by obtaining the P-rich biomass as adsorbents for enhanced Hg(II) removal and then charring the Hg-loaded biomass to prevent leaching of phosphate and to immobilize Hg(II). For algal surface modification, Scenedesmus obtusus XJ-15 were cultivated under different P concentrations and obtained the highest sites concentration of surface phosphoryl functional groups in 80 mg L^-1 P cultures. For Hg(II) adsorption, biomass from 80 mg L^-1 P cultures (B-80) achieved the highest saturated sorption capacity of 95 mg g^-1 fitting to Langmuir isotherm model under the optimum pH of 5.0. For charring stabilization, the Hg-loaded B-80 was calcinated under different temperatures, and the product obtained from 300 °C charring showed the lowest Hg(II) leaching rate without P release. Moreover, FT-IR and XPS analysis indicate that the surge of surface phosphoryl functional groups dominated the enhancement of Hg(II) sorption and also Hg(II) charring immobilization. The above results suggested that the developed strategy is promising for both phosphate and mercury removal from water and for co-immobilization of P and Hg(II) to prevent leaching.

Optimization of phosphate recovery as struvite from synthetic distillery wastewater using a chemical equilibrium model

This study investigates the feasibility of recovery of phosphorus via struvite precipitation from a synthetic anaerobically treated distillery spent wash by optimizing the process using a chemical equilibrium model, namely Visual MINTEQ. Process parameters such as Mg²⁺, [Formula: see text], and [Formula: see text] ion concentrations and pH were used as inputs into the model. Increasing the molar ratio of [Formula: see text] from 0.8:1 to 1.6:1 at pH 9 led to an increase in phosphate recovery from 88.2 to 99.5%. The model and experimental results were in good agreement in terms of phosphate recovery, indicating that the Visual MINTEQ model can be used to pre-determine the process parameters for struvite synthesis. Increasing the concentration of calcium ion adversely affected the synthesis and purity of struvite, whereas the presence of melanoidins had no significant impact. This study demonstrates that phosphorus recovery through struvite precipitation is a sustainable approach to reclaim phosphorus from high-strength industrial wastewater.

Effect of basic oxygen furnace slag addition on enhanced alkaline sludge fermentation and simultaneous phosphate removal

This study presents a promising approach that enhances the sludge fermentation by using basic oxygen furnace (BOF) slag as an alkaline source for the first time. BOF slag added to the reactors could maintain a stable alkaline condition due to continuous release of Ca(OH)₂ from slag. The reactor pH could be adjusted to a target value by the choice of the BOF slag dose. Concentrations of soluble chemical oxygen demand (sCOD) and short-chain carboxylates (SCCs) were substantially increased in the presence of BOF slag. At a BOF slag mass to sludge volume ratio of 1/10 g slag/L sludge, the reactor pH was maintained at 10 and the concentration of SCCs produced was the highest (i.e., 3510 mg COD L^-1 from 14,000 mg VS L^-1 of sludge mixture), followed by B/S ratios of 1/20, 1.50, 1/5, and 1/2.5 g slag L^-1 sludge with reactor pH of 9.4, 8.9, 10.5, and 11, respectively. Our data suggest that the pH value that best facilitates the degradation of sludge into SCCs and inhibit the conversion of SCCs into biogas is around 10. Interestingly, compositions of the accumulated SCCs varied greatly depending on the BOF slag dose. BOF slag showed phosphorus removal ability due to enhanced precipitation of Ca-PO₄^3--P complexes, which significantly lowered PO₄^3- concentration of the reactor effluent.

Preferable phosphate removal by nano-La(III) hydroxides modified mesoporous rice husk biochars: Role of the host pore structure and point of zero charge

Immobilizing La(OH)₃ nanoparticles (NPs) to porous hosts has been widely applied to inhibiting their inherent aggregation as well as the subsequent low utilization efficiency of La. In this study, a series of rice husk biochars (RHBCs) with high mesoporous rates were prepared and the effects of host pore structure and point of zero charge (pH_pzc) on phosphate adsorption by La-modified RHBCs was particularly focused. Characterization results confirmed that La(OH)₃ NPs were both confined in the pore channel and external surface of RHBCs. Adsorption kinetics and isotherms showed that La-modified RHBCs with higher mesoporous rates of the host showed a faster adsorption rate and La-modified RHBCs exhibited superior La utilization efficiency than many reported La-incorporated adsorbents. Phosphate could be effectively captured over a wide pH of 3-10 due to the high pH_pzc of La-modified RHBCs. Moreover, the La-modified RHBCs showed satisfactory affinity towards phosphate in the presence of coexisting anions and the phosphate adsorption by La-RHBC₉ was enhanced in the presence of Ca²⁺, while it was inhibited in the presence of Mg²⁺. The mesoporous structure of RHBCs strengthened the stability of La-modified RHBCs and weakened the inhibition of coexisting humic substances on phosphate adsorption through the "shielding effect".

Adsorption and mechanistic study for phosphate removal by magnetic Fe3O4-doped spent FCC catalysts adsorbent

The waste materials utilization has attained increasing attention due to the generation of a large number of spent materials. In the current study, a practical magnetic adsorbent (Fe₃O₄-doped spent Fluid Catalytic Cracking catalysts, abbreviated as FCC_x@(Fe)_y-O) was prepared, liable to be separated. The batch experiments were employed to investigate the phosphate removal behavior. The findings of this study demonstrated that FCC₄@(Fe)₁-O exhibited the best phosphate removal performance among the adsorbents (FCC_x@(Fe)_y-O), attributed to rough surface layer, i.e., composed of active sites. The various characterizations results revealed that the adsorption behavior of FCC₄@(Fe)₁-O followed the inner-sphere adsorption based on ligand exchanges mechanism. Furthermore, OH^- played an important role in the adsorption process. Minor effects were showed on the phosphate removal in the experiments of commonly coexisting anions, except CO₃^2- and SiO₃^2-. The above findings affirmed that FCC₄@(Fe)₁-O was a suitable adsorbent for phosphate removal in the practical application.

Enhanced phosphate removal from wastewater by using in situ generated fresh trivalent Fe composition through the interaction of Fe(II) on CaCO3

Excessive existences of nutrients such as phosphate in the aqueous environment remain as a heavy concern although many researches have been reported for dealing with their removal. Based on the understanding toward the interactions of Fe compounds with phosphate and carbonate from many available researches, we designed a very simple and efficient approach for phosphate removal by using in situ generated fresh trivalent Fe composition through the interaction of Fe(II) as FeSO₄ on CaCO₃. Addition and agitation of Fe(II) and CaCO₃ simultaneously to phosphate solution allowed an amorphous Fe(III)-P or Ca-Fe(III)-P precipitation, with a phosphate removal rate close to 100%, to reduce the residual phosphorus concentration less than 0.03 mg/L from 100 mg/L, reaching the discharge limit, even with the addition amounts of CaCO₃ as low as a stoichiometric ratio of CaCO₃/PO₄^3- at 0.9 and ratio of Fe(II)/PO₄^3- at 1.5, and the percent of P₂O₅ in the precipitate was as high as 19.4% enough as phosphate source for fertilizer production. Different from the alkaline process with enough OH^- group, the slow hydrolysis of CaCO₃ resulting in low concentration of OH^- group for the formation of Fe(OH)₂, which was oxidized soon by air into trivalent Fe, achieved a continuous generation of fresh ferric composition for phosphate precipitation and could avoid its rapid formation and subsequent transformation into stable FeOOH of large particle size to lose the activity. These results based on the synergistic effect of using CaCO₃ and Fe(II) together may have applications in the treatment of eutrophic wastewater through a process with many advantages of easy operation and low-cost besides the high removal efficiency with phosphate percentage inside the precipitate high enough to serve for fertilizer production.

Development of nanoscale zirconium molybdate embedded anion exchange resin for selective removal of phosphate

Development of a selective adsorbent with an enhanced removal efficiency for phosphate from wastewater is urgently needed. Here, a hybrid adsorbent of nanoscale zirconium molybdate embedded in a macroporous anion exchange resin (ZMAE) is proposed for the selective removal of phosphate. The ZMAE consists of a low agglomeration of zirconium molybdate nanoparticles (ZM NPs) dispersed within the structure of the anion exchange (AE) resin. As major results, the phosphate adsorption capacity of the ZMAE (26.1 mg-P/g) in the presence of excess sulfate (5 mM) is superior to that of the pristine AE resin (1.8 mg-P/g) although their phosphate uptake capacity was similar in the absence of sulfate and these results were supported by the high selectivity coefficient of the ZMAE toward phosphate over sulfate (S_PO4/SO4) more than 100 times compared to the pristine AE resin. This superior selective performance of the ZMAE for phosphate in the presence of sulfate ions is well explained by the role of the ZM NPs that contributed to 69% of the phosphate capacity which is based on an observation that the phosphate adsorption capacity of the ZM NPs is not affected by the presence of sulfate. In addition, the behavior of the selective phosphate removal by the ZMAE was well demonstrated by not only in the batch mode experiment with simulated Mekong river water and representative wastewater effluent but also in a column test.

Phosphate adsorption from aqueous solution by lanthanum-iron hydroxide loaded with expanded graphite

In this study, a novel adsorbent of expanded graphite loaded with lanthanum (III)-iron (III) hydroxide (EG-LaFe) was prepared for phosphate removal. The single factor of oscillating time, La/Fe molar ratio and total concentration of EG-LaFe were studied for optimization of preparation conditions. Effects of contact time, initial phosphate concentration, adsorption temperature and coexisting ions on the phosphate removal performance of EG-LaFe were investigated in detail. Adsorption kinetics and isothermal adsorption studies showed that the pseudo-second-order and the Langmuir model fitted the experimental data quite well. Thermodynamic analysis showed that the phosphate adsorption of EG-LaFe was spontaneous and endothermic. In addition, EG-LaFe exhibit high sorption selectivity toward phosphate over other coexisting ions. The phosphate adsorption mechanism was investigated by means of pH study, scanning electron microscopy and Fourier transform infrared spectroscopy. The results demonstrated that the probable mechanisms of phosphate adsorption on EG-LaFe were the replacement of surface hydroxyl groups (M-OH), electrostatic interaction and Lewis acid-base interaction.

Arsenate co-precipitation with Fe(II) oxidation products and retention or release during precipitate aging

The co-precipitation of arsenate (As(V)) with Fe(III)-precipitates is of great importance in water treatment and critically affects the fate of As in environmental systems. We studied the effects of dissolved phosphate (P; 0-1 mM), silicate (Si; 0 or 0.5 mM) and Ca (0, 0.5 and 4 mM) on the sequestration of 7 μM As(V) by Fe(III)-precipitates formed by the oxidation of 0.5 mM Fe(II) in aerated bicarbonate-buffered solutions with an initial pH of 7.0 as well as the retention or release of As(V) after precipitate aging for 30 d at 40 °C. Dissolved As(V) concentrations in fresh precipitate suspensions greatly varied as a function of the initial dissolved P/Fe ratio ((P/Fe)_init) and the concentrations of Ca and Si. Limited As(V) removal was observed at (P/Fe)_init that exceeded the critical ratio (P/Fe)_crit above which exclusively (Ca-)Fe(III)-phosphate forms. Effective As(V) removal was observed at (P/Fe)_init < (P/Fe)_crit, where initial formation of (Ca-)Fe(III)-phosphate is followed by the formation of Si-ferrihydrite in Si-containing electrolytes and of poorly-crystalline lepidocrocite and hydrous ferric oxide in the Si-free electrolytes. The retention of As(V) and P by fresh Fe(III)-precipitates was most effective in systems containing both Ca and Si. In the Si- and Ca-free electrolytes at (P/Fe)_init of ∼0.2-0.6, the rapid onset of precipitate aging with conversion of Fe(III)-phosphate to ferrihydrite resulted in a substantial remobilization of As(V) (up to 55% of initially precipitated As(V)). Ca reduced As remobilization during aging by stabilizing Ca-Fe(III)-phosphate and promoting Ca-phosphate formation, and Si by stabilizing Si-ferrihydrite against transformation. Consequently, also after aging, the lowest dissolved As(V) and P fractions were observed in precipitate suspensions containing both Ca and Si.

Investigation on mechanism of phosphate removal on carbonized sludge adsorbent

For the removal of phosphate (PO₄^3-) from water, an adsorbent was prepared via carbonization of sewage sludge from a wastewater treatment plant: carbonized sludge adsorbent (CSA). The mechanism of phosphate removal was determined after studying the structure and chemical properties of the CSA and its influence on phosphate removal. The results demonstrate that phosphate adsorption by the CSA can be fitted with the pseudo second-order kinetics and Langmuir isotherm models, indicating that the adsorption is single molecular layer adsorption dominated by chemical reaction. The active sites binding phosphate on the surface are composed of mineral particles containing Si/Ca/Al/Fe. The mineral containing Ca, calcite, is the main factor responsible for phosphate removal. The phosphate removal mechanism is a complex process including crystallization via the interaction between Ca²⁺ and PO₄^3-; formation of precipitates of Ca²⁺, Al³⁺, and PO₄^3-; and adsorption of PO₄^3- on some recalcitrant oxides composed of Si/Al/Fe.

Lanthanum oxide nanorods for enhanced phosphate removal from sewage: A response surface methodology study

Lanthanum-based adsorbents are ideal candidates for phosphate removal because of their excellent affinity to phosphate. However, their application in the removal of trace-levels of phosphate from sewage is still unsatisfactory due to the limited adsorption capacity and inadequate optimization of the operational parameters. To overcome these drawbacks, we have developed a novel lanthanum hydroxide (LH), using a facile precipitation and hydrothermal process that involves a nanorod-like structure with the lengths ranging from 124 to 1700 nm, depending on the La/OH molar ratio. The phosphate adsorption capacity of the developed LH is up to 170.1 mg-P g^-1 in synthetic water, while a slightly lower adsorption capacity of 111.1 mg-P g^-1 is observed in a sewage sample. A polynominal model consisting of three variables (i.e. dosage, reaction time and initial phosphate concentration) for predicting efficiency of phosphate removal has been successfully developed using a face-centred central composite design (CCD)-based methodology. The results also suggest a strong interactive effect of the dosage with the phosphate concentration, and reaction time, which can significantly affect the optimization of the phosphate removal by LH. Both X-ray photoelectron spectroscopy and X-ray diffraction studies indicate that the inner sphere complexation of phosphate with LH is probably the major mechanism governing phosphate removal.

Phosphate Removal During Conventional Hemodialysis: a Decades-Old Misconception

BACKGROUND/AIMS

Hyperphosphatemia is associated with high mortality rate in patients on dialysis. Conventional hemodialysis (HD) is a limit technique in removing phosphate (P). There is a widespread belief that P is removed mainly in the first hour of HD. The aim of this study was to certify the percentage of 1-hour removal of P as compared to the entire procedure.

METHODS

data from the first dialysis of the week of 21 patients (13 men, age 44±15 years), for 3 consecutive dialysis sessions were evaluated. Fresh dialysate samples were collected at 1 hour and at the end of the session from a partial spent dialysate collection method.

RESULTS

Pre dialysis serum P was 4.7±1.7 mg/dl. Reduction rate of serum P was 47.4 ± 14.3 and 45.1 ± 10.8% in 1- and 4-hour of HD, respectively (p=0.322). P removal was 194 (145, 242) mg in 1-hour (p<0.0001), which represents 25.0 ± 0.2% of the total removed during the entire HD. Patients with pre dialysis P ≥ 5.5mg/dl had higher P removal during HD than those with P < 5.5mg/dl [975 (587, 1354) vs. 776 (580, 784) mg, p=0.025], although the percentage of removal in 1 hour was not different from those with P < 5.5mg/d (24.9 ± 0.3 vs. 25.0 ± 0.1%, p=0.918). P removal during dialysis correlated with pre dialysis serum P (r=0.455, p=0.001), parathormone (r=0.264, p=0.037) and ultrafiltration volume (r=0.343, p=0.019).

CONCLUSION

despite the P serum concentration normalizing in the first hour of hemodialysis, the removal in the same period reaches only 25% of the entire session.

La3+/La(OH)3 loaded magnetic cationic hydrogel composites for phosphate removal: Effect of lanthanum species and mechanistic study

In this study, La³⁺(ion)/La(OH)₃-W/La(OH)₃-EW-loaded magnetic cationic hydrogel (MCH) composites were fabricated in situ and characterized to investigate the effects of lanthanum species on phosphate adsorption. The corresponding maximum P adsorption capacities of MCH-loaded La³⁺(ion) (MCH-La³⁺(ion)), La(OH)₃-W (MCH-La(OH)₃-W), and La(OH)₃-EW (MCH-La(OH)₃-EW) were 70.5 ± 2.67, 69.2 ± 3.5, and 90.2 ± 2.9 mg P/g, respectively. Furthermore, for MCH-La(OH)₃-EW, the P adsorption capacity was maintained relatively stable and high at pH 4.5-11 because of the ligand exchange, electrostatic interactions, and Lewis acid-base interactions. The enhanced adsorption of P was achieved over a wide pH range, as well as in the presence of competing anions (including Cl^-, NO₃^-, SO₄^2-, HCO₃^- and SiO₄^4-). Moreover, the exhausted MCH-La(OH)₃-EW could be easily regenerated by a NaOH-NaCl desorption agent with above 72% adsorption capacity remained during five recycles. The column adsorption capacity of MCH-La(OH)₃-EW reached ∼3500 bed volumes (BV) (∼67.7 mg P/g) as the concentration of P decreased from 5 mg/L to 0.1 mg/L. The ATR-IR, Raman, and XPS deconvolution results revealed that both MCH and lanthanum compounds, including La³⁺(ion), La(OH)₃-W and La(OH)₃-EW, contributed to the phosphate adsorption because of the electrostatic interactions between -N⁺(CH₃)₃ and phosphate, as well as the formation of LaPO₄·xH₂O.

Phosphorus removal performance and biological dephosphorization process in treating reclaimed water by Integrated Vertical-flow Constructed Wetlands (IVCWs)

Phosphorous removal in adsorption had been extensively researched; however, the biological dephosphorization process and optimum operating parameters have not been discussed or quantified in Integrated Vertical-flow Constructed Wetlands (IVCWs). In this study, IVCWs planted with different plants were employed to evaluate total phosphorus (TP) treatment performance under different hydraulic retention times (HRTs), in summer and autumn. The results showed that the systems planted with Canna generalis showed the highest TP removal efficiency (77%) under a three-day HRT in autumn. The activities of exopolyphosphatase (PPX) and polyphosphate kinase (PPK) were determined, and it was found that PPK activity was seasonably variable and had been more active in autumn than that in summer (p<0.05). Highly significant correlation was revealed between PPK activity and TP removal efficiency (p<0.05). The 16S rDNA high-throughput sequencing results indicated that Pseudomonas genus might be the main participant in phosphorus aerobic biological adsorption in IVCWs.

Genetic improvement of Magnetospirillum gryphiswaldense for enhanced biological removal of phosphate

OBJECTIVES

To improve its phosphate accumulating abilities for phosphate recycling from wastewater, a magnetotactic bacterium, Magnetospirillum gryphiswaldense, was genetically modified to over-express polyphosphate kinase.

RESULTS

Polyphosphate kinase was over-expressed in the bacterium. The recombinant strain accumulated ninefold more polyphosphate from synthetic wastewater compared to original wild type. The magnetic property of the recombinant M. gryphiswaldense strain was retained.

CONCLUSIONS

The recombinant M. gryphiswaldense can be used for phosphate removal and recovery in bioremediation.

Effectiveness of phosphate removal during anaerobic digestion of waste activated sludge by dosing iron(III)

Phosphate-Fe(II) precipitation induced by Fe(III) reduction during the anaerobic digestion of excess activated sludge was investigated for the removal of phosphorus and its possible recovery. The experiments were conducted with three Fe(III) sources at 35 °C and 55 °C. The results show that ferrihydrite-Fe(III) was effectively reduced during the anaerobic sludge digestion by 63% and 96% under mesophilic and thermophilic conditions, respectively. Whereas FeCl₃-Fe(III) was only mesophilically reducible and the reduction of hematite-Fe(III) was unnoticeable at either temperature. Efficient precipitation of vivianite was not observed although high saturation index values, e.g., >14 (activity reduction not considered), had been reached. This reveals the complexity of vivianite precipitation in anaerobic digestion systems; for example, Fe(II) complexation and organic interference could not be ignored. With ferrihydrite amendments at a Fe/TP of 1.5, methane production from sludge digestion was reduced by 35.1% at 35 °C, and was unaffected when the digestion temperature went up to 55 °C. But, acidic FeCl₃ severely inhibited the methane production and consequently the sludge biomass degradation.

Recovery of phosphorus from synthetic wastewaters by struvite crystallization in a fluidized-bed reactor: Effects of pH, phosphate concentration and coexisting ions

The crystallization of struvite in fluidized-bed crystallizer (FBC) was performed to treat synthetic wastewaters that contain phosphorous. Under optimal conditions (pH 9.5, molar ratio Mg/N/P = 1.3/4/1, struvite seed dose (53-297 μm) = 30 g L^-1, total flow rate = 12 ml min^-1, reflux = 120 ml min^-1), the removal of phosphate (PR) and the crystallization ratio (CR) were 95.8% and 93.5%, respectively. Based on a thermodynamic prediction, the supersaturation, which was obtained from the difference between the theoretical solubility and phosphate concentration, predominated the crystallization efficiency and the properties of the struvite pellets, such as their morphology, particle size and apparent density. Coexisting ions NO₃^- (80, 160 ppm), CH₂COOH^- (260, 520 ppm), F^- (650, 1300 ppm) and SO₄^2- (650, 1300 ppm), were utilized to prepare P-containing wastewaters. Of these ions, SO₄^2- (1300 ppm) remarkably reduced the capability of FBC to remove phosphate from solution. In the presence of NO₃^- and CH₃COO^- (for synthesizing TFT-LCD wastewater), and F^- and SO₄^2- (for synthesizing semiconductor wastewater), CR% was lower than in pure water, although the ultimate PR% did not differ significantly.

Phosphate removal by lead-exhausted bioadsorbents simultaneously achieving lead stabilization

Low-cost adsorbents have been continuously developed for heavy metal removal, but little information is available concerning the follow-up treatment of the toxic metal-laden adsorbents. In this study, an optional strategy was provided for the further treatment of heavy metal-impregnated low-cost adsorbents through employing them for phosphate retention. The enhancement of phosphate adsorption by the sorbed lead was first validated using several types of raw or modified waste biomass. Tea waste-supported hydrated manganese dioxide (HMO-TW) with the highest Pb sorption capability was then chosen to systematically evaluate phosphate retention. Phosphate adsorption onto lead-laden HMO-TW (HMO-TW(Pb)) was pH-insensitive with only slight decline at pH > 8.5, and was barely affected by competing anions owing to the specific surface precipitation mechanism. Moreover, no signs of lead leakage from HMO-TW(Pb) were observed during phosphate adsorption at a wide pH range (4.2-11.3) and high ion strength (0-250 mg L^-1 NaNO₃). The lead on HMO-TW(Pb) was greatly stabilized through phosphate retention, which also reduced the environmental risks of their following treatment such as solidification and landfill. Additionally, the phosphate adsorption onto HMO-TW(Pb) was quick (with equilibrium time <60 min) and barely affected by temperature. Fixed-bed column test further suggested that HMO-TW(Pb) has practical applicability in efficient removal of phosphate from water.

Beyond feast and famine: Selecting a PHA accumulating photosynthetic mixed culture in a permanent feast regime

Currently, the feast and famine (FF) regime is the most widely applied strategy to select for polyhydroxyalkanoate (PHA) accumulating organisms in PHA production systems with mixed microbial cultures. As an alternative to the FF regime, this work studied the possibility of utilizing a permanent feast regime as a new operational strategy to select for PHA accumulating photosynthetic mixed cultures (PMCs). The PMC was selected in an illuminated environment and acetate was constantly present in the mixed liquor to guarantee a feast regime. During steady-state operation, the culture presented low PHA accumulation levels, likely due to low light availability, which resulted in most of the acetate being used for biomass growth (Y_x/s of 0.64 ± 0.18 Cmol X/Cmol Acet). To confirm the light limitation on the PMC, SBR tests were conducted with higher light availability, at similar levels as would be expectable from natural sunlight. In this case, the Y_x/s reduced to 0.11 ± 0.01 Cmol X/Cmol Acet and the culture presented a PHB production yield on acetate of 0.67 ± 0.01 Cmol PHB/Cmol Acet, leading to a maximum PHB content of 60%. Unlike other studied PMCs, the PMC was capable of simultaneous growth and PHB accumulation continuously throughout the cycle. Thus far, 60% PHA content is the maximum value ever reported for a PMC, a result that prospects the utilization of feast regimes as an alternative strategy for the selection of PHA accumulating PMCs. Furthermore, the PMC also presented high phosphate removal rates, delivering an effluent that complies with phosphate discharge limits. The advantages of selecting PMCs under a permanent feast regime are that no aeration inputs are required; it allows higher PHA contents and phosphate removal rates in comparison to FF-operated PMC systems; and it represents a novel means of integrating wastewater treatment with resource recovery in the form of PHA.

Phosphate removal from aqueous solution using ZVI/sand bed reactor: Behavior and mechanism

This research reports on phosphate removal from aqueous solution using ZVI/sand packed columns. The influence of column preconditioning, consisting of ZVI pre-oxidation before feeding the columns with phosphate solution, revealed that a column aged for 1 day was more efficient than un-conditioned column, 5-days and 10-days preconditioned columns. The distribution of phosphate trapped inside the columns was evaluated by measuring phosphate concentration in the solids at different levels (P1, P2 and P3) along the depth of the columns. The distribution of phosphate inside the columns was determined for a time period up to 46 days, corresponding to column saturation. Results showed heterogeneous trapping along the column before saturation and homogeneous distribution upon saturation. The maximum cumulative trapped phosphate after column dismantling was determined before saturation (after 17 days running) at 130, 68 and 31 mgP/gFe at the inlet-P1, P1-P2 and P2-P3 layers, respectively, whereas the homogeneous distribution of phosphate upon saturation was determined at 132 mgP/gFe throughout the column. Solid supports were characterized using SEM, XRD and XPS. Lepidocrocite and maghemite/magnetite were the only iron oxidation products identified at the different layers inside the columns. XPS results confirmed the sorption of phosphate at the surface of ZVI and its oxidation products and highlighted the formation of an iron phosphate complex.

Potential of cyanobacterial biofilms in phosphate removal and biomass production

Four cyanobacterial biofilms, raised from cyanobacterial mats and dominated by Phormidium and Oscillatoria spp., were successfully grown attached to polyester mesh discs, and were tested for their probable application in [Formula: see text] -P removal from domestic sewage and other nutrient enriched wastewaters. Biofilm # 2, dominated by Phormidium fragile, best removed [Formula: see text] -P; nevertheless, some of it also grew outside the substrate making harvesting difficult. Other biofilms also efficiently removed [Formula: see text] -P from the medium in the following order: Biofilm # 1 > Biofilm # 3 > Biofilm # 4. Their growths were restricted to discs and are therefore better candidates as they can be efficiently harvested after [Formula: see text] -P removal. [Formula: see text] -P removal was primarily due to its uptake during growth of the biofilm rather than because of precipitation as pH of the medium remained <8.5. [Formula: see text] -N concentration in the medium determined [Formula: see text] -P removal efficiency of the test biofilms and therefore optimum N:P ratio is necessary for optimizing [Formula: see text] -P removal. The test biofilms could also efficiently remove [Formula: see text] -N from the medium.

CeO2-covered nanofiber for highly efficient removal of phosphorus from aqueous solution

The lowering phosphorus concentration of lakes or rivers using adsorbents has been considered to be the most effective way to prevent water eutrophication. However, the development of an adsorbent is still challenging because conventional adsorbents have not shown a sufficient phosphorus adsorption capacity (0.3-2.0mmol/g) to treat industrial, agricultural or domestic wastewater at a large scale. Herein, a novel and effective strategy to remove phosphorus efficiently with a CeO2-covered nanofiber is shown. The CeO2-covered nanofiber was synthesized through (1) amine group immobilization onto an electrospun polyacrylonitrile nanofiber and (2) adsorption of Ce(3+) on it. The CeO2-covered nanofiber played a role in catching phosphate ions in an aqueous solution by the oxidation, reduction, and ion-exchange of adsorbed Ce(3+) on the nanofiber from CeO2 to CePO4, and enabled remarkable phosphate adsorption capacity of the nanofiber (ca. 17.0mmol/g) at the range of ca. pH 2-6. Our strategy might be the most feasible method to efficiently lower the phosphorus concentration in lakes or rivers owing to the easy and inexpensive preparation of CeO2-covered nanofiber at an industrial scale, with a high phosphate adsorption capacity.

Removal of phosphorus by a high rate membrane adsorption hybrid system

Membrane adsorption hybrid system (MAHS) was evaluated for the removal of phosphate from a high rate membrane bioreactor (HR-MBR) effluent. The HR-MBR was operated at permeate flux of 30L/m(2)h. The results indicated that the HR-MBR could eliminate 93.1±1.5% of DOC while removing less than 53% phosphate (PO4-P). Due to low phosphate removal by HR-MBR, a post-treatment of strong base anion exchange resin (Dowex(∗)21K-XLT), and zirconium (IV) hydroxide were used as adsorbent in MAHS for further removal of phosphate from HR-MBR effluent. It was found that the MAHS enabled to eliminate more than 85% of PO4-P from HR-MBR effluent. Hence, HR-MBR followed by MAHS lead to simultaneous removal of organics and phosphate in a reliable manner. The experiments were conducted only for a short period to investigate the efficiency of these resins/adsorbents on the removal of phosphorus and high rate MBR for organic removal.

Preferable removal of phosphate from water using hydrous zirconium oxide-based nanocomposite of high stability

In this study, we employed a new nanocomposite adsorbent HZO-201, which featured high stability under varying solution chemistry, for preferable removal of phosphate from synthetic solution and a real effluent. An anion exchange resin (D-201) was employed as the host of HZO-201, where nano-hydrous zirconium oxide (HZO) was encapsulated as the active species. D-201 binds phosphate through nonspecific electrostatic affinity, whereas the loaded HZO nanoparticles capture phosphate through formation of the inner-sphere complexes. Quantitative contribution of both species to phosphate adsorption was predicted based on the double-Langmuir model. Preferable removal of phosphate by HZO-201 was observed in the presence of the competing anions at higher levels (Cl(-), NO3(-), SO4(2-), HCO3(-)). Fixed-bed adsorption indicated that the effective volume capacity of a synthetic water (2.0 mg P-PO4(3-)/L) by using HZO-201 was ∼1600 BV in the first run (<0.5mg P-PO4(3-)/L), comparable to Fe(III)-based nanocomposite HFO-201 (∼1500 BV) and much larger than D-201 (<250 BV). The exhausted HZO-201 can be in situ regenerated by using a binary NaOH-NaCl solution for cyclic runs, whether fed with the synthetic solution or real effluent. In general, HZO-201 is a promising alternative to Fe(III)-based adsorbents for trace phosphate removal from effluent particularly at acidic pH.

Granulation and ferric oxides loading enable biochar derived from cotton stalk to remove phosphate from water

Granulation of biochar powder followed by immobilization of ferric oxides on the macroporous granular biochar (Bg-FO-1) substantially enhanced phosphate removal from water. BET analysis confirmed that both granulation and ferric oxides loading can increase the surface areas and pore volumes effectively. Bg-FO-1 was proven to be a favorable adsorbent for phosphate. The phosphate adsorption capacity was substantially increased from 0 mg/g of raw biochar powder to 0.963 mg/g (Bg-FO-1). When the ferric oxides loading was prior to granulation, the adsorption capacity was decreased by 59-0.399 mg/g, possibly due to the decrease of micropore and mesopore area as well as the overlaying of binders to the activated sites produced by ferric oxides.